1. Field of the Invention
The present invention relates to a non-contact type IC card using an electromagnetic wave as a communication medium, and a non-contact type IC card system employing this non-contact type IC card.
2. Description of the Related Art
FIG. 43 shows a general arrangement of a known non-contact type IC card system including a non-contact type IC card where an electromagnetic wave is employed as a communication medium. In the illustration, the IC card system comprises a non-contact type IC card (which will hereinafter be referred to as a card) 1, a reader/writer (abbreviated as R/W) unit 2, and a host computer 3 being in connection with the R/W unit 2. That is, the non-contact type IC card employed system usually comprises the card 1, the R/W unit 2 operative to read and write data from and to the card, and the host computer 3 responsible for control of the whole system. Both the R/W unit 2 and host computer 3 can be constructed as one unit (R/W unit). The transmission and reception of the data between the card 1 and the R/W 2 are made using an electromagnetic wave as a medium.
However, such a prior non-contact type IC card system thus arranged does not produce satisfactory results for meeting requirements: (1) a batteryless card not requiring a built-in battery is necessary with a view to reducing its manufacturing cost, being released from the battery life, and coping with serious environmental problems; (2) depending upon the application fields, the received signal level will vary in accordance with the communication distance, i.e., the distance between the card and the R/W unit, whereupon the reception level is required to be adjustable at the card side; (3) in addition to effective power transmission and reception, the reduction of power consumption (demand) to the utmost is necessary for realizing long-distance communications with a batteryless card; (4) for communications from the R/W unit to the card, data transmission will be made simultaneously with power supply, while phase modulation or frequency modulation is needed because continuous power supply is impossible in amplitude modulation, and at this time demodulation with less current consumption needs to be carried out at reception in the card side; and (5) upon the reception of the transmitted data in the R/W unit side, the power transmission to the card side can once be stopped, for which reason the card needs to effectively operate only on the energy accumulated at power supply for the transmission of a necessary amount of data and, hence, to effectively execute the modulation.